Overall objectives are to understand the structure-taste relationship of taste-active molecules by X-ray crystallographic methods. Goals set for the current year have been the collection of X-ray diffraction data for the monellin native crystal and a few heavy atom derivatives and locate the heavy atom positions if possible. In addition, structure of several "bitter-sweet" pairs of compounds (each pair consisting of two chemically related compounds, one sweet, the other bitter) will be determined to understand the critical and configurational differences responsible for the different taste.